公开(公告)号：US20170233847A1

公开(公告)日：2017-08-17

申请号：US15502264

申请日：2015-08-07

Applicant: ArcelorMittal

Inventor： Jean-Philippe Masse ,  Jean-Christophe Hell

IPC: C21D9/46 ,  C21D1/19 ,  C21D1/18 ,  C23C2/02 ,  C23C2/12 ,  C23C2/40 ,  C23C2/06 ,  C22C38/38 ,  C22C38/34 ,  C22C38/06 ,  C22C38/02 ,  C23F17/00 ,  B32B15/01 ,  C25D3/56 ,  C25D3/22 ,  C21D1/26

CPC classification number: C21D9/46 ,  B32B15/012 ,  B32B15/013 ,  C21D1/185 ,  C21D1/19 ,  C21D1/26 ,  C21D2211/001 ,  C21D2211/002 ,  C21D2211/005 ,  C21D2211/008 ,  C22C38/02 ,  C22C38/06 ,  C22C38/34 ,  C22C38/38 ,  C23C2/02 ,  C23C2/06 ,  C23C2/12 ,  C23C2/40 ,  C23F17/00 ,  C25D3/22 ,  C25D3/565

Abstract: The invention relates to a method for producing a high strength coated steel sheet having a yield stress YS>550 MPa, a tensile strength TS>980 MPa, and improved formability and ductility. The steel contains: 0.15%≦C≦0.25%, 1.2%≦Si≦1.8%, 2%≦Mn≦2.4%, 0.1%≦Cr≦0.25%, Al≦0.5%, the balance being Fe and unavoidable impurities. The sheet is annealed at a temperature between TA1=Ac3−0.45*(Ms−QT) and TA2=830° C. for at least 30s then quenched by cooling it to a quenching temperature QT between 180° C. and 300° C., then heated to a partitioning temperature PT between 380° C. and 480° C. and maintained at this temperature for a partitioning time Pt between 0 sec and 300 sec, then either hot dip coated and cooled to the room temperature with a cooling rate of at least 25° C./s below 300° C., or directly cooled to the room temperature with a cooling rate of at least 25° C./s and further electro-galvanized, or cooled to the room temperature with a cooling rate of at least 25° C./s without coating. The steel according to the invention contains 5% to 25% of intercritical ferrite, at least 50% of partitioned martensite, at least 10% of residual austenite, less than 10% of fresh martensite, and bainite, the sum of partitioned martensite and bainite being at least 60%. It also relates to the obtained coated or non coated sheet.